Direct radiative forcing of urban aerosols over Pretoria (25.75°S, 28.28°E) using AERONET Sunphotometer data: First scientific results and environmental impact
Journal of Environmental Sciences (China)
Discipline of Physics, School of Chemistry and Physics, College of Agriculture, Engineering and Science, University of KwaZulu-Natal, Westville Campus, Durban, South Africa; Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing, China; Optronic Sensor Systems, Council for Scientific and Industrial Research (CSIR)-DPSS, Pretoria, South Africa
The present study uses the data collected from Cimel Sunphotometer of Aerosol Robotic Network (AERONET) for the period from January to December, 2012 over an urban site, Pretoria (PTR; 25.75°S, 28.28°E, 1449mabove sea level), South Africa. We found that monthly mean aerosol optical depth (AOD, τa) exhibits two maxima that occurred in summer (February) and winter (August) having values of 0.36±0.19 and 0.25±0.14, respectively, high-to-moderate values in spring and thereafter, decreases from autumn with a minima in early winter (June) 0.12±0.07. The Angstrom exponents (α440-870) likewise, have its peak in summer (January) 1.70±0.21 and lowest in early winter (June) 1.38±0.26, while the columnar water vapor (CWV) followed AOD pattern with high values (summer) at the beginning of the year (February, 2.10±0.37cm) and low values (winter) in the middle of the year (July, 0.66±0.21cm). The volume size distribution (VSD) in the fine-mode is higher in the summer and spring seasons, whereas in the coarse mode the VSD is higher in the winter and lower in the summer due to the hygroscopic growth of aerosol particles. The single scattering albedo (SSA) ranged from 0.85 to 0.96 at 440nm over PTR for the entire study period. The averaged aerosol radiative forcing (ARF) computed using SBDART model at the top of the atmosphere (TOA) was -8.78±3.1W/m2, while at the surface it was -25.69±8.1W/m2 leading to an atmospheric forcing of +16.91±6.8W/m2, indicating significant heating of the atmosphere with a mean of 0.47K/day. © 2014 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
Atmospheric aerosols; Atmospheric radiation; Environmental impact; Optical properties; Sea level; Solar radiation; AERONET; Aerosol optical depths; Pretoria; Radiative forcings; Single scattering albedo; Urban growth; aerosol; albedo; atmospheric forcing; environmental impact; light scattering; optical depth; radiative forcing; urban atmosphere; Gauteng; Pretoria; South Africa; aerosol; aerosol; analysis; atmosphere; chemistry; environment; light related phenomena; remote sensing; South Africa; weather; Aerosols; Atmosphere; Environment; Optical Phenomena; Remote Sensing Technology; South Africa; Weather